Recovery of petroleum naphthalene



July 10, 1962 A. c. McKlNNls RECOVERY OF' PETROLEUM NAPHTI-IALENE Filed April 4, 1960 ZEO.

United States Patent Ofice 3,043,890 Patented July 10, 1962 3,043,890 RECOVERY F PETROLEUM NAPHTHALENE Art C. McKinnis, Long Beach, Calif., assigner to Union Oil Company of California, Los Angeles, Calif., a corporation of California Filed Apr. 4, 1960, Ser. No. 19,526 8 Claims. (Cl. 1260-674) This invention rel-ates to new methods for the recovery and purification of naphthalene contained in various hydrocarbon fractions derived from petroleum or-the like. More particularly, the method comprises Vsubjecting the hydrocarbon fraction t0 azeotropic distillation with butyrolactone, whereby non-naphthalenic hydrocarbons boiling in the naphthalene range are azeotroped overhead as a minimum boiling azeotrope with the butyrolactone. It has been found that substantially all of the non-naphthalenic aromatic hydrocarbons contained in these petroleum fractions, and `boiling Within the 400-450 F. range, can be efficiently azeotroped out of the mixture before any substantial amounts of naphthalene are distilled overhead. Following removal of the non-naphthalenic hydrocarbons, the naphthalene contained in the remaining bottoms fraction can -then be easily recovered by nonazeotropic distillation, or by any other desired means.

It is known th-at naphthalene fractions containing likeboiling paraflin hydrocarbons can be purified by azeotropic distillation With various `azeotroping agents. However, a more diflicult problem of separation is involved in this invention, in that the petroleum fractions dealt with are contaminated mainly with aromatic hydrocarbons such as alkyl benzenes, alkyl tetralins, alkyl indanes and the like, boiling within the naphthalene range and lthereabouts, e.g., from about 400-450 F. Petroleum fractions of this nature can be derived from various hydrocarbon conversion and refining processes commonly used in the industry, eg., catalytic reforming, catalytic crack` ing, thermal cracking and the like. In particular, catalytic reforming of naphthas produces a heavy reformafte fraction boiling above about 400 F., which may contain 40-80% of naphthalene and methyl naphthalenes. The

' remaining hydrocarbons in this fraction are largely -alkyl benzenes, tetralins, indanes and the like. Sometimes a significant proportion of naphthenes are present, but usually little if any parains. The recovery of pure naphthalene from such petroleum fractions presents ya difiicult problem.

Attempts have been made in the past to recover pure naphthalene from such fractions by first subjecting them to catalytic hydrodealkylation to convert the methyl naphthalenes to naphthalene, and then recovering the naphthalene by fractional distillation. None of these methods are entirely satisfactory, In fractional crystallization, eutectics are formed which place severe .limitations upon the yields of pure naphthalene which can be recovered. Solvent extraction is diliicult and expensive Where the contaminants are also mainly aromatic in character. Simple fractional distillation is also impractical because of .the close proximity of boiling points of the contaminating hydrocarbons, and also the formation of complex azeotropes. Avoiding these major difiiculties., and providing an efficient azeotroping agent for purifying these naphthalenefractions, constitute the principal objects of this invention.

It has now been found Ithat butyrolactone is a rem-ark- *s r hydrocarbons, and condensed into separator 12.

fore any substantial amounts of naphthalene appear in the overhead. Moreover, it is found that the azeotropic overhead is unexpectedly rich in hydrocarbons, containing only about 20-50% by Weight of butyrolactone, thus minimizing the distillation load, and the amount of azeotroping agent required. Another important advantage resides in the excellentstability of butyrolactone in the system.

Reference is now made to FIGURE 1 of the accompanying drawing, which illustrates schematically one mode of applying the process of this invention. The initial feedstock is brought in through line 2 and admitted to distillation column 4 wherein the primary azeotropic distillation takes place. Column 4 may be a conventional fractional distillation column containing, e.g., 20-80 plates and may be operated at overhead reflux ratios of, eg., 1:1 to 20:1. Azeotroping is continued until essentially all the non-naphthalenic hydrocarbons boiling within about 10 F., and preferably 20 F., of naphthalene, are distilled overhead. The overhead temperatures during `azeotropic distillation will usually range between about 370 and 400 F., butyrolactone itself boiling at 401 F. The azeotropic overhead is taken olf through line 6 and condensed in condenser S, and the resulting condensate is transferred via line 10 to a liquid-liquid phase separator 12. To provide the desired reux ratio, a portion of the condensate in line 10 may be diverted through line 16 and 'admitted to the top of column 4.

In phase separator 12, the condensate may separate spontaneously' into Itwo phases, or a small proportion of a miscibility-reducing agent may be required, depending upon the nature of the feed. If the feed is rich in lower alkylatcd aromatics a miscibility-reducing -agent is ordinarily required, but if it is rich in higher alkylated aromatics and/0r in naphthenes, adequate phase separation occurs spontaneously. Suitable miscibility-reducing .agents include butyrolactone-miscible anti-solvents for hydrocarbons (e.g., Water), or hydrocarbon-miscible tanti- `solvents for butyrolactone, eg., paraffinic or naphthenic hydrocarbons such as pentane, decane, cyclohexane `and the like. Preferably, the miscibility-reducing agent vshould be easily separable, as by distillation, from the phase in which it is dissolved. Water is ordinarily prefer-red, and is used in amounts up to about 10% by Weight of the butyrolactone, but any small amount is effective in some degree.

The solvent-rich phase which `stratiies in separator 12 Will ordinarily contain about 1 to 25% of dissolved hydrocarbons, and this solution, if it is free of water, is conltinuously recycled via line 14 back to a mid-point in distillation col-umn 4. However, if water is used in separator 12, the wet solvent is preferably diverted via line 9' to a small distillation column 11, from Which Water is distilled overhead via line 13 and returned to separator 12 via line 10. Water-free solvent is withdrawn as bottoms via `line 15 and returned to column 4 via line 14. The wet butyrolactone can be returned directly to azeotroping column 4, with some sacrifice of column efficiency The hydrocarbon-rich phase in separator 12 ordinarily will contain about 1 to 15% by Weight of dissolved butyrolactone. This hydrocarbon-rich phase is then transferred via line 18 to fractionating column 20, from which all of the butyrolactone is distilled overhead via line 22 as an azeotrope with a portion of the non-naphthalenic The non-naphthalenic hydrocarbons are withdrawn as bottoms from column 20 via line 24. s

A naphthalene-containing bottoms fraction is continuously withdrawn from azeotroping column 4 via line 26, and transferred to naphthalene fractionating column 2S; Since all of the close-boiling non-naphthalenic hydrocarbons have been removed in column 4, the principal separationwhich is achieved in column 2S is the separation of naphthalene from methyl naphthalenes. The pure naphthalene overhead is withdrawn via line 30 and condensed in cooler 32 to form pure white naphthalene crysvtialsmelting at 80| C., 'and is ordinarily in excess of 99% pure. The methyl naphthalene bottoms from column 28 is withdrawn via line 34 and may be sent to dealkylation facilities not shown to produce additional naphthalene.

The foregoing is not to be considered as limiting the scope of the process. Those skilled in the art will understrand that other conventional azeotroping techniques may be employed, and other conventional methods such as fractional crystallization may be employed to recover naphthalene from the azeotroping bottoms.

It is to be noted that butyrolactone also forms an azeotrope with naphthalene, but no difficulty is experi- Venced in obtaining adequate azeotrope fractionation in column 4, due to the difference in boiling points of the respective -azeotropes. If desired, column 28 can also be operated as an azeotropic distillation with butyrolactone, in which case a less efficient column is required since the naphthalene-butyrolactone azeotrope boils lower than naphthalene itself.

The feedstocks which may be treated herein include a wide variety of aromatic petroleum fractions. They may comprise heavy catalytic naphtha fractions, dealkylated light catalytic cycle oils, dealkylated coker distillates, heavy reformate fractions asV well as the products of dealkylation thereof, and many similar materials. All lof lthese fnactions contain substantial proportions of'one or more of the troublesome -alkyl benzenes, alkyl tetralins, and alkyl indanes boiling in the 40G-450 E. range. They, mayalso contain naphthenes and parafns, but these contaminants cause no substantial diificulty. Y

The present invention has particular utility for the treatment of hydrocarbon fractions of the aforesaid types containing uaphthalenefractions comprising naphthaleneV and non-naphthalenic hydrocarbon materiall boiling within F. thereof, and especially petroleum fractions Vwithin the above categoryin which the naphthalene fraction boils over the entire range of about 4l0450 P. and comprises one or more of the alkyl benzenes, alkyl tetralins and alkyl indanes as the non-naphthalenic hydrocarbon material. More specifically, petroleum fractions within the above class which have been found particularly amenable to treatment by the method of this invention are those boiling above about 400 F. which include, as non-naphthalenic hydrocarbons, alkyl benzenes, alkyl Vtetrdins and alkyl indanes boiling over the entire range of about 414434 F.; heavy naphtha reformates boiling above about 400 F. and including a naphthalene fraction boiling over the entire range of about 410-450 F. which preferably contains yalkyl benzenes, alkyl tetralins and alkyl indanes; and heavy naphtha reformates which have been subjected to catalytic hydrodealkylation,

boiling over aboutV 400 F. and including a naphthalene fraction boiling overthe entire ran-ge of about 410-450 F., which naphthalene fraction perferably contains alkyl benzenes, alkyl tetralins and alkyl indanes.

Ordinarily, it is preferred to remove the light endsl from the feed, boiling below about 410 F., since these lighter fractions contain very little naphthalene. The end-boiling point of the fraction -is not critical herein, but will ordinarily range between about 450 and 600 F. The dealkylation process referred to herein may consist of any conventional catalytic hydrodealkylation. An especially preferred technique for dealkylating methyl naphthalenes employs steam and hydrogen at elevated temperatures `and pressures over a kcobalt molybdate catalyst,`as is more particularly described in U.S. Patent No. 2,734,929 to Doumani.

The eifectivenessof the process is more .particularly illustrated inthe following examples, which are not however to be construed as limiting in scope.

This example demonstrates the improved recoveryY of non-naphthalenic hydrocarbons Where azeotroping with butyrolactone, as compared to straight fractional distillation. The feed was a blend of platinum reformate ends and catalytic cracked gasoline ends, the blend boiling over the range of about 400-5 5 0 F. (true boiling points). A hydrocarbon type analysis showed the following approximate composition (weight percent):

A sample of this feed was subjected to azeotropic distillation with butyrolactone in a t0-plate Oldershaw column at 10:1 reflux ratio, and the naphthalene content of incremental portions of overhead was measured. After 20% of the feed had distilled over, the hydrocarbon component of the overhead still contained less than 0.08% of naphthalene, and even at 30% overhead, the naphthalene content was less than 1%. Curve A of FIGURE 2 shows graphically the very slowly rising naphthalene con- 'tent of the azeotropic overhead, while Curve B, representing the same distillation carried out in the absence of butyrolactone, shows that the initial ,overhead contains more than 10% of naphthalene, and none of the first 25% of overhead contained less naphthalene than the feed. It is thus evident that butyrolactone is a remarkably eiiicient and selective azeotroping lagent for this type of feed, while simple fractional distillation is completely impractical.

' EXAMPLE Il A. In an attempt to isolate pure naphthalene by simple fractionation from a platinum reformate bottoms fraction which had been subjected to catalytic hydrodealkylation (to convert methyl naphthalenes to naphthalene), 700 grams of the dealkylated product (containing about 39% naphthalene) was subjected to careful fractionation in a 60-plate Oldershaw column at a 20:1 reflux ratio. Twenty-three separate overhead cuts were taken, and the melting points of the richest naphthalene cuts were deters mined. Theresults were as follows:

Table 1 Overhead Wt. of Melting Cut; Temp., cut, Gms. Point,

27o-406 124 421 27. 6 424 19. l 156. 5 426 23.1 169 427 24. 0 173. 5 427 29.8 173. 5 428 37. 7 173. 5 425 19.5 171.0 425 26.0 174.0 425 18. 5 173.0 426 19. 9 172.0 426 18.0 168. 0 428 18. 7 164. 0 430 9. 2 445-466 188. 3 468 12. 8 23 80. 0 Botts 11.5

Since the melting point of pure naphthalene is 179-l80 F., it will be apparent that none of the naphthalene cuts taken were more than about -95% pure. In order to compare the distribution of hydrocarbon types during Vdistillation, cuts 1-7 were combined into a cumulative frac-I 5 tion A, cuts 8-20 into cumulative fraction B, and cuts 21423 into cumulative fraction C, and each cumulative fraction was analyzed for the major hydrocarbon types. The results were as follows:

Thus, it is apparent that alkyl benzenes, tetralins, indanes and naphthenes are spread throughout all the fractions, and distillation alone is ineffective for the recovery of pure naphthalene.

B. In contrast to the above, another portion (295 gms.) of the dealkylated `feed mixture was blended with 255 gms. of the un-dealkylated feed of Example I, and the blend was fractionated in the same column at a 5:1 reflux ratio, in the presence of 300 gms. of -butyrolactone After 37% by weight of the hydrocarbon feed had been aZeot-roped overhead (final overhead temperature, 392 E), the remaining `bot-toms fraction was washed with Water, dried, and subjected to lfractional distillation at 5:1 refiux ratio. After discarding -a small forerun, eight separate cuts of naphthalene overhead were collected and melting points determined, with the following results:

Table 3 OverheadA Wt. of Melting Cut Temp., out, Gms. Point,

O F' Q `Cuts l-8 represent 99j-% pure naphthalene, and since the aggregate amount of these cuts was 100.2 gms., and

the feed contained 131 gms. of naphthalene, the yield of 50 this pure naphthalene was over 76.5%.

It will thus be apparent that the process of this invention gives a remarkably `eficient recovery of pure naphthalene fromV the petroleum fractions here concerned. Separations similar to those shown in the examples are achieved when other petroleum fractions within the purview of the invention are employed. The invention is @i hence not limited to the details of the examples, but only as dened in the following claims:

I claim:

1. A method for the recovery of substantially pure naphthalene from a petroleum fraction boiling above about 400 F., which comprises: (l) subjecting said fraction to yazeotropic distillation in admixture with butyrolactone until substantially all the non-naphthalenic hydrocarbons in said fraction which boil within about 10 F. of naphthalene are distilled overhead as an azeotrope with said butyrolactone, Iand (2) recovering substantially pure naphthalene from the remaining bottoms fraction.

2. A method as defined in claim 1 wherein said nonnaphthalenic hydrocarbons comprise at least one hydrocarbon type from the class consisting of alkyl benzenes, alkyl tetralins, and alkyl indanes..

3. A method as defined in claim 1 wherein said nonnaphthalenic hydrocarbons include alkyl benzenes, alkyl tetralins and alkyl indanes boiling over the entire range of about 414-434 F.

4. A method as defined in claim 1 wherein said petroleum fraction is a heavy naphtha reformate including a naphthalene `fraction boiling over the entire range of about 410450 F.

5. A method as defined in claim 1 wherein said petroleum fraction is a heavy naphtha reformate which has been subjected to catalytic hydrodealkylation, and includes a naphthalene fraction boiling over the entire range of about 4l0-450 F.

6. A method for the recovery of substantially pure naphthalene from a petroleum distillate including a naphthalene fraction boiling over the entire range of about 410-450 F., said naphthalene fraction also containing alkyl benzenes, alkyl tetralins and alkyl indanes, which comprises: (l) subjecting said fraction to azeotropic distillation in admixture with butyrolactone until substantially all the non-naphthalenic hydrocarbons in said fraction which boil within about 20 F. of naphthalene are distilled overhead `as an azeotrope with said butyrolactone, Vand (2) distilling the remaining bottoms fraction in the absence of butyrolactone to recover substantially pure naphthalene overhead.

7. A method as defined in claim 6 wherein said petroleum fraction is a heavy naphtha reformate boiling above about 400 F.

8. A method as dened in claim 6 wherein said petroleum fraction is a heavy naphtha reformate which has been subjected to catalytic hydrodealkylation, and boiling above about 400 F.

References Cited in the iile of this patent UNITED STATES PATENTS 2,831,905 Nelson Apr. 22, 1958 FOREIGN PATENTS 804,221 Great Britain Nov. 12, 1958 

1. A METHOD FOR THE RECOVERY OF SUBSTANTIALLY PURE NAPHTHALENE FROM A PETROLEUM FRACTION BOILING ABOVE ABOUT 400*F., WHICH COMPRISES: (1) SUBJECTING SAID FRACTION TO AZEOTROPIC DISTILLATION IN ADMIXTURE WITH BUTYROLACTONE UNTIL SUBSTANTIALLY ALL THE NON-NAPHTHALENIC HYDROCARBONS IN SAID FRACTION WHICH BIOL WITHIN ABOUT 10*F. OF NAPHTHALENE ARE DISTILLED OVERHEAD AS AN AZEOTROPE WITH SAID BUTYROLACTONE, AND (2) RECOVERING SUBSTANTIALLY PURE NAPHTHALENE FROM THE REMAINING BOTTOMS FRACTION. 